This application claims the priority of Korean Patent Application No. 2003-97244, filed on Dec. 26, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a voltage reference generating circuit, and more particularly, to a CMOS exponential function generating circuit with a temperature compensation technique
2. Description of the Related Art
In general, a variable gain amplifier (VGA), which is a block circuit in the component of an automatic gain controlled (AGC) circuit, provides a variable gain that is linearly proportional to the applied control voltage on a decibel (dB) scale.
When designing a variable gain amplifier, the most important thing that has to be considered is the possibility of accurately controlling a gain according to an applied control voltage. Such gain control is enabled by an accurate exponential function as the relationships between current and voltage of a bipolar transistor embedded within the variable gain amplifier.
In addition, a conventional variable gain amplifier is composed of CMOS circuits which allow this amplifier to be easily and conveniently integrated with other circuits, and the gain is adjusted by an exponential the characteristics of a parasitic bipolar transistor in the CMOS process technology.
However, in the CMOS variable gain amplifier, the value of a threshold voltage of a metal oxide semiconductor (MOS) device is changed due to a process deviations, temperature variations, and noises of a power supply voltage. Therefore, since the values of both an input signal and an output signal of the CMOS variable gain amplifiers are limited, it is difficult to smoothly operate the CMOS variable gain amplifier. In other words, since the operation of the CMOS variable gain amplifier depends highly on process variables, temperature, and a power supply voltage, it is very difficult for the variable gain amplifier with an accurate exponential function to be integrated.